Main menu: Restart logo animation when displayed

[wjt]

Previously the logo was animated once, then stayed on its last frame.
I think it's nice to reshow the animation when moving back from the
credits or options screens.

Add the necessary API to AnimatedTextureRect to make this work.

[wjt]

I'm happy to be disagreed with on this one! I have just had versions of this patch lying around in my local clone for months, so decided to finish it to see if others agree that this is good.

[github-actions]

Play this branch at https://play.threadbare.game/branches/endlessm/wjt/main-menu-restart-logo-animation-when-displayed/.

(This launches the game from the start, not directly at the change(s) in this pull request.)

[manuq]

I'm happy to be disagreed with on this one! I have just had versions of this patch lying around in my local clone for months, so decided to finish it to see if others agree that this is good.

I find it a bit too much to also play the animation when going back from Options or Credits, to be honest. But is only a matter of taste. Feel free to merge it!

[wjt]

Ok, I trust your judgement! In that case I will revise this PR to keep the new features in AnimatedTextureRect but preserve the old behaviour